Highly ordered semiconducting metal oxide nanorod arrays on transparent and flexible substrates are promising materials for modern optoelectronic and electronic devices, such as touch screens, flexible displays, and printable electronics components. Herein, a modified nanocrystal-seed-directed-hydrothermal route has been developed to achieve the large-scale growth of aligned and dense SnO₂ nanorod arrays on a single side of free-standing reduced graphene sheets (rGss) which forms two-layered heterostructures of SnO₂/rGss benefical for fabrication of potential devices. Based on in situ TEM studies, while utilizing integrated STM and AFM holders, mechanical robustness of SnO₂ nanorods and rGss complexes, their low resistance and Ohmic contacts at the heterostructure interfaces were confirmed. An electron source device using a flexible graphene substrate and the above heterostructures has then been fabricated that shows outstanding field emission properties: a threshold field value as low as 1.06 V μm⁻¹, and an emitting current density as high as 1.1 A cm⁻² at an applied field of 7.5 V μm⁻¹, suggesting an ideal energy provider as well as an energy-saving device. This would open up possibilities for the extensive study of the interesting properties from these most promising nanostructures and extend their practical applications in the energy field.